FIG. 1 is a block diagram for showing a typical example of a conventional GPRS.
Mobile radio terminals 1, 2, such as cellular telephones, respectively exist in location areas of subscriber switchboard stations 1, 2. The mobile radio terminal 1 is connected with a subscriber switchboard station 22 by radio. The mobile radio terminal 2 is connected with a subscriber switchboard station 23 by radio. The subscriber switchboard stations 22, 23 are connected with a gateway relay switchboard station 21. The gateway relay switchboard station 21 is connected with a home location register (HLR, hereinafter) 31 for managing informations on subscribers, and with an internet service provider (ISP, hereinafter) 41. The ISP 41 is connected with the HLR 31 via the gateway relay switchboard station 21. The gateway relay switchboard station 21, the subscriber switchboard stations 22, 23, and the HLR 31 form the GPRS 100.
In the GPRS shown in FIG. 1, when the mobile radio terminal 1 desires to transmit a packet data 50 to the mobile radio terminal 2, the mobile radio terminal 1 requires the gateway relay switchboard station 21 to approve transmission of the packet data 50 via the subscriber switchboard station 22. The gateway relay switchboard station 21 transmits the packet data 50 to the ISP 41. In the above description, the destination of the packet data 50 is not necessarily restricted to the ISP 41, and may be the other network or the other packet network.
When the packet data 50 directed to the mobile radio terminal 2 is delivered to the gateway relay switchboard station 21 via the ISP 41, the gateway relay switchboard station 21 inquires of the HLR 31 about a subscriber switchboard station in a location area of which the mobile radio terminal 2 exists. If it becomes clear that the mobile radio terminal 2 exists in the location area of the subscriber switchboard station 23, the gateway relay switchboard station 21 notifies the subscriber switchboard station 23 of arrival of the message. The gateway relay switchboard station 21 carries out paging for calling the mobile radio terminal 2 up via the subscriber switchboard station 23, establishes a route for transmitting the packet data 50 to the mobile radio terminal 2, and executes transmission of the packet data 50 directed to the mobile radio terminal 2. Thereafter, transmission and reception of the packet data 50 between the mobile radio terminals 1, 2 are also performed via the ISP 41.
FIG. 2 shows the other example of the conventional GPRS.
In the GPRS shown in FIG. 2, the mobile radio terminals 1, 3 exist in the same location area 11 of the subscriber switchboard station 22. In the system shown in FIG. 2, when the mobile radio terminal 1 desires to transmit the packet data 50 to the mobile radio terminal 3, the packet data 50 is transmitted to the ISP 41 in the first place, after the mobile radio terminal 1 requires the gateway relay switchboard station 21 to start transmission of the packet data 50 directed to the mobile radio terminal 3 via the subscriber switchboard station 22. When the packet data 50 directed to the mobile radio terminal 3 is delivered to the gateway relay switchboard station 21 via the ISP 41, the gateway relay switchboard station 21 inquires of the HLR 31 about a subscriber switchboard station in a location area of which the mobile radio terminal 3 exists. If it becomes clear that the mobile radio terminal 3 exists in the location area of the subscriber switchboard station 22, the gateway relay switchboard station 22 notifies the subscriber switchboard station 22 of arrival of the packet data 50. The gateway relay switchboard station 21 carries out paging for calling the mobile radio terminal 3 up via the subscriber switchboard station 22, and establishes the route for transmitting the packet data 50 to the mobile radio terminal 3. Thereafter, transmission and reception of the packet data 50 between the mobile radio terminals 1, 3 are always performed through the ISP 41.
The GPRS disclosed in Japanese Patent Applications, Laid-Open, No. 10-13904 has a structure similar to that shown in FIG. 1, in which the plural mobile radio terminals are placed under the command of the same gateway relay switchboard station. In the former system, the gateway relay switchboard station assigns packet addresses to the respective mobile radio terminals dynamically, and the packet addresses of the limited number are utilized efficiently.
However, according to the GPRS shown in FIGS. 1, 2, since the standard of the communication system is so constructed that the packet data can not be directly transmitted and received between the mobile radio terminals even when they are placed under the command of the same GPRS, the data packet is necessarily transmitted and received therebetween via the external network, such as the ISP. As a result, the packet data must trace a roundabout route even in the same GPRS, and it sometimes occurs that the packet data is lost or delayed. This problem cannot be solved by the GPRS proposed in Japanese Patent Applications, Laid-Open, No. 10-13904.